Older gardeners have been warned to wash their hands after using compost
following research that found disease-causing strains of Legionella bacteria
in potting soil on sale in Britain.

Scientists have proposed introducing prominent hygiene advice labels on bags after discovering Legionella bugs in 14 of the 22 brands of compost they tested.

Most of the bacteria did not pose a risk to humans, but four of the composts contained Legionella longbeachae, which can in rare cases cause Legionnaires’ disease, a severe form of pneumonia which sometimes leads to hospital admission and death.

Health experts say that the risk is “very low” for young and healthy people, but have advised gardeners to avoid wear gloves when handling compost, avoid breathing in the dust and wash their hands immediately afterwards.

A recent outbreak in Scotland linked to Legionella longbeachae in compost has left six people infected since August, with some needing hospital intensive care.

Dr Tara Beattie, from the University of Strathclyde in Scotland, who led the new research, said it was “not too surprising” that species of Legionella were found in compost sold in the UK because disease-causing bacteria are widespread in the environment.

However, she suggested that moves to phase out the use of peat in compost for environmental reasons could lead to greater incidence of Legionella longbeachae and therefore more infections.

Compost sold in Britain is increasingly composed of sawdust and bark, which have traditionally been used to produce potting soils in Australia and New Zealand, where cases of Legionella associated with compost are more common.

Dr Beattie’s findings are reported in the journal Clinical Microbiology and Infection, although her paper does not name the brands of compost that were tested.

She said a larger-scale survey covering a wider range of composts was needed to determine whether Legionella bacteria were as widespread as her initial study suggested.

"It should be emphasised though, that although Legionella seem to be common in compost, human infection is very rare, especially if you consider the volume of compost sold and used,” she added.

"But with any potential source of infection precautions should always be taken. The occurrence of these bacteria in composts in Australia and New Zealand, and the cases of infection that have been traced to compost has resulted in hygiene warnings on compost packaging in these countries, and this is something manufacturers in the UK may wish to consider.”

Australia introduced prominent warning labels on compost bags about the risk of Legionnaires' disease and the importance of good hygiene in 2003, and New Zealand followed suit two years later.

Health Protection Scotland has recommended that the Scottish government should require a similar measure.

Public Health England says in advice on its website: “The evidence from Australia suggests that avoiding inhalation of dust or moisture droplets and good standards of personal hygiene when handling compost and soil may be associated with a lower risk of Legionnaires’ disease.

“There is currently insufficient data to properly quantify the extent of the risk that compost and potting soils may pose.

“However, the risk is likely to be very low for the healthy and younger elements of the population, and compost should be treated like soil and high standards of personal hygiene encouraged.”